我们可以通过实现ResultSetHandler接口或扩展ResultSetHandler的任何现有实现来创建我们自己的自定义处理程序.在下面给出的示例中,我们通过扩展BeanHandler类创建了一个自定义处理程序EmployeeHandler.
为了理解与DBUtils相关的上述概念,让我们编写一个将运行的示例读取查询.要编写我们的示例,让我们创建一个示例应用程序.
Step | 描述 |
---|---|
1 | 更新文件 MainApp.java . |
2 | 编译并运行应用程序,如下所述. |
以下是
public class Employee { private int id; private int age; private String first; private String last; private String name; public int getId() { return id; } public void setId(int id) { this.id = id; } public int getAge() { return age; } public void setAge(int age) { this.age = age; } public String getFirst() { return first; } public void setFirst(String first) { this.first = first; } public String getLast() { return last; } public void setLast(String last) { this.last = last; } public String getName() { return name; } public void setName(String name) { this.name = name; }}
以下是 EmployeeHandler.java 文件的内容.
import java.sql.ResultSet;import java.sql.SQLException;import org.apache.commons.dbutils.handlers.BeanHandler;public class EmployeeHandler extends BeanHandler{ public EmployeeHandler() { super(Employee.class); } @Override public Employee handle(ResultSet rs) throws SQLException { Employee employee = super.handle(rs); employee.setName(employee.getFirst() +", " + employee.getLast()); return employee; } }
以下是 MainApp.java 文件的内容.
import java.sql.Connection;import java.sql.DriverManager;import java.sql.SQLException;import org.apache.commons.dbutils.DbUtils;import org.apache.commons.dbutils.QueryRunner;import org.apache.commons.dbutils.ResultSetHandler;import org.apache.commons.dbutils.handlers.BeanHandler;public class MainApp { // JDBC driver name and database URL static final String JDBC_DRIVER = "com.mysql.jdbc.Driver"; static final String DB_URL = "jdbc:mysql://localhost:3306/emp"; // Database credentials static final String USER = "root"; static final String PASS = "admin"; public static void main(String[] args) throws SQLException { Connection conn = null; QueryRunner queryRunner = new QueryRunner(); DbUtils.loadDriver(JDBC_DRIVER); conn = DriverManager.getConnection(DB_URL, USER, PASS); EmployeeHandler employeeHandler = new EmployeeHandler(); try { Employee emp = queryRunner.query(conn, "SELECT * FROM employees WHERE first=?", employeeHandler, "Sumit"); //Display values System.out.print("ID: " + emp.getId()); System.out.print(", Age: " + emp.getAge()); System.out.print(", Name: " + emp.getName()); } finally { DbUtils.close(conn); } } }
创建源文件后,让我们运行应用程序.如果你的申请一切正常,它将打印以下信息.
ID: 103, Age: 28, Name: Sumit, Mittal